What kind of Clay makes a good mold?

Question: What kind of Clay makes a good mold!?

I want to make a mold for a bunch of silver scrap that I have laying around!. I've used cuttle bone before but it is really hard to work detail into a bone mold!. I was thinking clay would be nice but I don't know if it works, or what kind I would need!. Is there something other than clay that I can use!? Thanks in advance!.Www@QuestionHome@Com

Best Answer - Chosen by Asker:

for metal, I would say silicone!. It's non toxic, easy to use, flexable and it can make a mold good for metal, (although you won't get as many castings from it as you would for resins) ti can take the heat of molten metals!. most synthetic clays can't!.

Cilinart's a good place to get silicone!. http://www!.culinart!.net/silicone!.html
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While silicone rubbers are good up to several hundred degrees, I wouldn't trust them to the melting point of silver!. Check with maker before hand!. The cheapest reliable way is to make your model in wax and use a 50-50 mix of plaster of paris and silica flour, both of which you can buy in smaller quantities, while investment comes in 33 pound, etc!.
Both the 50-50 and investment have to be supported in a sleeve (flask) and heated slowly before use to drive off both mechanically and chemically held water!.
If you are going to carve into the clay, you can use gray potters clay if you can fire it to a setting higher than 1200F before bringing it to casting temp which is 800F for siliver http://users!.ticnet!.com/mikefirth/meltme!.!.!.Www@QuestionHome@Com

Instead of clay look at investment materials

Here is a link to a company that makes the material for jewelry casting

http://www!.ransom-randolph!.com/html/jewe!.!.!.Www@QuestionHome@Com

Aiken clay!.Www@QuestionHome@Com